The present invention relates to an error correction system used in a picture transmission which uses an inter-frame coding for information suppression in a video transmission system such as a televideo conference system, and/or a videophone which handles moving pictures.
In a moving picture transmission system using an inter-frame coding for information suppression, a picture signal is divided into blocks each of which has a predetermined code length, or the picture signal is transmitted for each predetermined area portion. The example of the former is shown in Japanese patent application No. 33782/1986, and a conventional asynchronous transfer mode (ATM).
In such a transmission system, a picture area in a received picture frame is sometimes lost due to an error of an address of a transmission block, loss of transmission blocks, and/or traffic overflow in multiplexing transmission modes. When a picture area is lost in an inter-frame coding system, correct decoding becomes impossible unless the lost picture area is compensated.
Conventionally, when a picture area is lost, the succeeding receive data after the lost picture area is disregarded, and the decoding operation stops. Then, the transmitter side switches the coding mode an entire picture frame from the inter-frame coding to the intra-frame coding which uses only the data in the same picture frame. Alternatively, transmission blocks are classified to important blocks which significantly affect decoded pictures, and less important blocks which do not significantly affect decoded pictures.
When a transmission block is lost in the prior art, a decoded moving picture stops for a significant portion of time, and therefore, a decoded moving picture becomes unnatural. Further, the coding efficiency is seriously deteriorated due to intra-frame coding of the entire picture frame.